I posted this to the psychology community in response to someone who asked about animals experiencing mental health symptoms. Thought I'd post it here just because I wrote it.
I don't know of any official research. However, I am a hurricane survivor, and I can tell you about my experiences with my cats.
I moved to Florida in 2002 and took my then six-year-old cat, Inca, into a multi-cat household for the first time. I did not expect her to do well. She hid for a while and was territorial; but we people made a point to define space for ourselves and our cats, and the cats settled into a routine and took to the space with no complaints. In 2003, I acquired an additional cat and took on care for one of Inca's rivals when one of the roommates moved away. The transfer of Sable to "our" territory went fairly smoothly, although she and Inca maintain a healthy distance. Both cats coexist peacefully with Sierra. Inca coexisted peacefully with one of my roommate's cats and fought regularly with the other. I often wondered how much of their fighting was healthy sociability.
In 2004, I boarded the cats during Hurricane Charley. They were housed in a single 5 x 8 enclosure at a facility which boarded 400 animals that weekend. Charley did not even rain on us in St. Pete. When I brought them home, they were clingy and would not leave "our space" (my bedroom), even with the door open. Three weeks later, we rode out Frances at home. At the end of that week, I flew them here to Indiana, and we moved into an apartment owned by my parents which I had rented previously.
Inca seemed at first to settle in easily. She slept in her old spots, was very social, meowed when I spoke to her, came to her name, etc. But after about three weeks here, she stopped eating and became completely unresponsive to vocalizations. She slept very deeply. and wouldn't even startle when I approached. I took her to the vet to see if she was showing age-related problems. He said she was in excellent health and her ears were fine. When she was awake, she startled appropriately if someone clapped their hands behind her.
She wouldn't go to the food bowl--in fact, she rarely left her chair except to go to the litter box. So I fed her by hand at the same time every evening and turned it into a bonding routine. I sat on the floor near her and petted her while she ate. I moved the feeding place once in a while to encourage her to venture out from the chair a bit. So sometimes I fed her in front of the couch, and sometimes I fed her across the room from the chair. After a couple of weeks sne began to come asking for the food. I considered this a major improvement. Eventually, I started adding a little water to a bowl of food to entice her to eat from the bowls again, and in time I moved her to the bedroom and gradually took away the "special" food so that she began eating out of the feeder with Sable and Sierra again.
Over the next six to eight weeks, she gradually regained her sociability and now responds again to my vocalizations. She started sleeping on the beds again instead of solely in her chair. She started fighting with Sable again. As much as I hate it when they fight, it really bothered me that Inca was so lethargic! She still loves her chair, but she doesn't sleep so deeply and if I come into the room she will often mew at me to acknowledge me. She is very sensitive to anything upsetting in the environment, including my panic attacks, and she will still signal me to go into the living room where I used to feed her. She will accept pets as comfort now in lieu of food, although I still allow her an occasional treat there just because.
The vet said it was very possible that Inca could have experienced PTSD symptoms related to the stress of boarding, hurricane, and move. That's really a lot of stuff to put a little cat through in a short amount of time. I've known animals to grieve the loss of companions before--we had a dog who would go outside repeatedly just to look for the cat in her lounging spot after the cat died, and when the dog would come back in the dog would whimper and shed tears. In this move, Inca had lost one of her rivals. If my theory holds true that rivalry provides a healthy form of sociability for cats, this would have been a significant loss for Inca.